The present invention relates to a process and a device for measuring the attenuation of a line. It applies in particular to the rating of asymmetric digital subscriber lines (ADSL).
Certain telephone operators are seeking to develop ADSL technology so as to offer their subscribers higher Internet transmission throughputs. However, the telephone lines of the networks of these operators are in part not reliable enough to ensure good transmission at these throughputs. These operators have therefore to determine which part of their network can support these transmission throughputs. Hitherto, this determination is based on a theoretical calculation of the attenuation of the electric lines. This calculation makes it possible to determine the average attenuation of the electric lines as a function of their lengths and of their diameters. The maximum theoretical length of the line which can support these transmission throughputs is determined from this attenuation. Knowing the length of the telephone lines of its network, the operator can theoretically determine which part of the network supports throughputs compatible with ADSL technology. Telephone lines having unmodeled defects, the theoretical limits are greater than the actual limits. Operators therefore adopt a safety margin, for example by taking half the theoretical limit, so as to be certain that the lines selected support ADSL technology.
A drawback of this technique is that a part of the network which could support high transmission throughputs is not utilized. In order to utilize the greatest number of lines, that is to say to bring ADSL technology to the maximum of subscribers, it is necessary to carry out measurements of attenuation at 300 kHz. These attenuation measurements make it possible to rate the ADSL lines.
In the known techniques for measuring the attenuation of a line, two technicians are sited at the ends of said line. The first technician emits an electric signal having a known amplitude, the second technician measures the electric signal received at the other extremity of the line. The ratio of the amplitude of the signal emitted to the amplitude of the signal received is the attenuation of the line. A drawback of this technique is that it is expensive since it requires two technicians who have to go to each end of the lines to be tested.
An aim of the invention is to alleviate the aforesaid drawbacks, and in particular to make it possible to measure the attenuation of an electric line from a measurement carried out at one end of the line only, and to do so in an economical manner.
Accordingly, the invention relates to a process and a device for measuring the attenuation of a line. The measurement process according to the invention makes it possible to measure the attenuation of a line at a given frequency F and comprises at least the following steps:
(a) the emission of an electric signal at one end of the electric line, said signal comprising a spectral component of amplitude A1 at the frequency F;
(b) the measurement of the signal reflected by the other end of the line, at the end of the line from where the signal was emitted;
(c) the determination of the amplitude A2 of the spectral component at the frequency F of the reflected signal;
(d) the determination of the attenuation of the line from the ratio of the amplitude A2 to the amplitude Al, the electric signal being emitted for a duration less than the outward and return time of a wave on the line, so as to preclude interference between the signal emitted and the signal reflected during the measurement.